The present invention relates to a refrigerator oil composition. More particularly, the present invention relates to a refrigerator oil composition which is thermally and chemically stable in the presence of halogen-containing refrigerants and further which has superior lubricating and sealing properties.
A base oil derived from naphthenic crude oil of high quality has heretofore been widely used as a refrigerator oil because of its superior characteristics. However, the naphthenic crude oil is shortage and tends to gradually decrease in the world, and it is said that, in particular, special naphthenic crude oil for use in the preparation of a refrigerator oil will be exhausted in the future. Under these circumstances, it has become increasingly difficult to ensure such naphthenic crude oil. It is therefore inevitably necessary to make good use of low quality naphthenic base oil containing relatively large amounts of impurities, paraffinic base oil, and other synthetic base oils.
The main characteristics generally required for the usual refrigerator oil are: (1) it has an appropriate viscosity; (2) it is superior in low temperature performance; (3) the critical temperatures at which it is dissolved in refrigerants are low; (4) it produced good results in the sealed tube test; and (5) it is superior in thermal stability, i.e., produces good results in the panel coking test.
The most serious problem encountered in making use of low quality naphthenic base oil or paraffinic base oil as a refrigerator oil is that the stability of the refrigerator oil as prepared therefrom is very poor when brought into contact with halogen-containing refrigerants; that is, its ability to inhibit the formation of hydrogen halide, such as hydrogen chloride, resulting from the reaction with the halogen-containing refrigerants is very low.
To improve such poor stability, various stabilizers have been proposed, including glycidyl ether type epoxy compounds such as phenyl glycidyl ether and octylepoxy stearate, and epoxidized fatty acid monoesters (see Japanese Patent Application Laid-Open Nos. 132,005/1978, 140,469/1978 and 58,298/1980, and U.S. Pat. No. 2,582,084).
The stability of the refrigerator oil has not yet become satisfactory even by using such stabilizers, and it is now very difficult to produce a high performance refrigerator oil from base oils other than high quality naphthenic base oil.